This invention relates to a method and apparatus for inspecting articles of manufacture and, more particularly, relates to a method and apparatus for automatically inspecting such articles using video cameras and strobed momentary light beams.
Methods and apparatus for the inspection of articles of manufacture with video cameras is known. An example of such a method and apparatus are disclosed in U.S. Pat. No. 4,025,201. This patent discloses a method and apparatus in which the light is directed through an article on at least two different light paths to create two images that are directed upon a single, video camera. Preferably, decussate paths of light are generated with the article to be inspected placed at the intersection of the decussate light paths and with reflecting means to redirect the decussate light paths and their images onto the video camera at separate locations to permit the camera to view the images of each light path. Since both the images of the article can be scanned for defects, the entire area of the article or glass container may be scanned for defects during a single inspection period. The light beams may be generated by a single source used in connection with a reflective beam splitter to produce the decussate light paths, or two light sources may be used to produce the decussate beams. The preferable sources of light provide pulsed illumination which is substantially collimated.
U.S. Pat. No. 4,380,025 discloses another video inspection system for glass bottles in which the video signal of a video camera is electronically processed to determine defects in the bottles. This patent addresses the problem of rejecting satisfactory glassware articles because of images created by decorative bottle portions within the inspection region and the edges of the bottle, particularly at the shoulders of the bottle. In the system of U.S. Pat. No. 4,380,025, an artificial blanking unit is provided to inhibit inspection in variable blanking areas within the inspection region that can be positioned to correspond to the shoulders and decorated areas of the bottles. Inspection is inhibited within the blanking areas by artificial trigger pulses generated within the blanking area to generate an inhibit defect signal.
Another inspection apparatus is disclosed in U.S. Pat. No. 2,798,605. In U.S. Pat. No. 2,798,605, bottles are passed along a conveyor line and are passed in front of an optical system of a television camera. As each object passes in front of a camera, a light flash of short duration is provided to thereby illuminate the object and cause an image to be transmitted to the mosaic of a television camera tube. The mosaic is scanned by the cathode-ray gun of the camera tube which provides an output signal that indicates appreciable discontinuity in the video signal from its average level.
The above systems employ a video camera including a vidicon tube of a type known in the art. In the vidicon, the light image from the article being inspected is optically focused onto a photo-conductive target located at the face plate of the vidicon tube. At the target, this light produces an electrical-charge pattern corresponding to the various light intensities in the image on the target. By replenishing the charge deficiencies with electrons from a beam that scans the target, the light pattern is converted into a time sequence of current variations which is the video signal.
The scanning of the target is accomplished by swinging the electron beam across the target in a series of lines that are displaced vertically and in time into two interlaced individual rasters. The electron beam, in scanning the target, sweeps the target vertically at a rate of 60 hertz, while simultaneously sweeping it horizontally at the rate of 15,750 hertz.
The scanning electron beam is generated by the radiant heating of a cathode with a filament. The scanning beam is accelerated toward the photoconductive target with a fixed voltage of, for example, 350 volts, and is directed electrically within the vidicon in a trajectory that is nearly perpendicular to the target and is electromagnetically focused on the target.
During its unblanked scanning, the current variations in the electron beam are converted into voltage variations which are referenced to a compensated black level, are blanked during the intervals in which the scanning beam retraces horizontally and vertically across the target, are clipped at white and black peaks to obtain a usable signal between such extremes, are mixed with a signal to synchronize the scanning of the CRT of a television receiver, and are amplified to provide a composite video signal.
During the horizontal retrace at the end of each line and during the vertical retrace at the end of each raster field, the scanning electron beam is blanked, or turned off, to prevent the generation of unwanted noise to be added to the video signal. Normally, the electron beam is switched off with horizontal and vertical blanking pulses applied to the cathode of the image tube during the retrace intervals. The horizontal and vertical pulses and biasing potential used to turn off the scanning beam are developed by the normal camera circuits associated with a vidicon camera tube.
Video inspection systems of the type above, for example, described in the above-identified patents using strobed light sources to provide a bright field, have been, in the past, very sensitive in their ability to distinguish between the detection of such defects in glassware as birdswings, stuck glass, blisters, and the like. Such systems are difficult to adjust to reliably distinguish between satisfactory and flawed glassware.